Re: [users] Bug in Rnd function (StarBasic)?

[Andrew Douglas Pitonyak]

I changed your code and recieved a very different answer. Consider the 
following:

Sub RndTest0
   Dim i As Long
   Dim Count1 As Long, Count2 As Long
   Dim Value As Double
   Dim one As Double
   Dim ExecTime As Long
   one = 1.0
   ExecTime=Timer
   Randomize
   For i=1 To 1000000
       Value=Rnd
       If Value<0.99999 Then
           Count1=Count1+1
           If Value=one Then
               Count2=Count2+1
           Endif
       EndIf
   Next i
   ExecTime=Timer-ExecTime
   Print "Rnd>0.99999 occured "+Count1+ _
         " times, Rnd=1 occured "+Count2+ _
         " times. This was calculated in "+ExecTime+" s."
End Sub
Note: I used type Long rather than Integer to avoid round off.
Second, I did not compare to "1", which is an integer, but rather, I 
stored 1.0 in a variable and compared to that. I could have also 
compared against "1.0". This version NEVER returns a value of 1.0.

Johnny Andersson wrote:
I found that the Rnd function returns values (0.00000... to 
1.00000...),  not (0.00000... to 0.99999...), which would be better in 
most cases.

Example:
Dim MyInteger As Integer
Dim MyArray(1 To 6) As Integer
Randomize
MyInteger=Int(6*Rnd)+1 'Supposed to return numbers 1 to 6, byt may now 
and  then return 7. Happened to me many times.
MyArray(MyInteger)=MyArray(MyInteger)+1 'Causes an error message if  
MyInteger>6 which may happen in this case.

In this example Rnd returns 1.
Sub RndTest
    Randomize 30091
    Print Rnd
End Sub
This example took about 2 minutes to run on my PC (450 MHz P2, a few 
other  applications were running at the same time):

Sub RndTest0
    Dim i As Long
    Dim Count1 As Integer, Count2 As Integer
    Dim Value As Double
    Dim ExecTime As Long
    
    ExecTime=Timer
    Randomize
    For i=1 To 1000000
        Value=Rnd
        If Value>0.99999 Then
            Count1=Count1+1
            If Value=1 Then
                Count2=Count2+1
            Endif
        EndIf
    Next i
    ExecTime=Timer-ExecTime
Print "Rnd>0.99999 occured "+Count1+" times, Rnd=1 occured "+Count2+"  
times. This was calculated in "+ExecTime+" s."
End Sub

It seems like every time Rnd>0.99999 then Rnd=1, so even though Rnd  
produces 15 decimals it seems like only 5 (or less) are relevant. When 
I  tried Rnd=1 at 20 to 34 occasions (different result different times 
of  course) which indicates that Rnd=1 about once every 29000 to 50000 
times.

Anyway, is Rnd=1 supposed to ever happen or is this a bug?

--
Andrew Pitonyak
My Macro Document: http://www.pitonyak.org/AndrewMacro.sxw
My Macro Book: http://www.hentzenwerke.com/catalog/oome.htm
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